This is the first in a series of reviews of the state of public opinion for each of the parties to coincide with the conference season. By pooling together all the available polling evidence we can reduce the impact of the random variation each individual survey inevitably produces. Most of the short term advances and setbacks in party polling fortunes are nothing more than random noise; the underlying trends – in which we are interested and which best assess the parties’ standings – are relatively stable and little influenced by day-to-day events. If there can ever be a definitive assessment of the parties’ standings, this is it. Further details of the method we use to build our estimates of public opinion can be found here.

UKIP’s annual conference, which kicks off in Birmingham today, does not normally attract much attention. The Eurosceptic right wing party has in the past been dismissed as an ineffective fringe organisation, whose impressive results in European Parliament elections, used by British voters to vent their frustrations with Brussels and Westminster alike, would never translate into serious domestic political influence.

This year is different. The party written off not so long ago by the current Prime Minister as a collection of ‘loonies, fruitcakes and racists’ has surged in the polls, and in outlets as diverse as the Guardian, the Daily Mail and Radio 4′s Today programme journalists debate its potential influence on the outcome of the next election. Our first chart estimating UKIP support since the last election, pooling all the available evidence, confirms that a growing share of the electorate are now turning to the purple people. The party’s support has grown in two spurts. The first came at the end of 2010 and beginning of 2011, when UKIP support roughly doubled from around 2% to 4%. The most likely cause was the greatly elevated visibility of the EU, which was in the news nearly continuously during this period due to serial debt crises culminating in bailouts to Greece (May 2010); Ireland (November 2010) and Portugal (May 2011). Withdrawal from the EU is UKIP’s signature issue, so it is easy to see why endless stories of debt and despair in the Eurozone increased the party’s appeal).

After the Portugese bailout in May 2011, the Eurozone faded from the headlines for a while, and UKIP’s support levelled off at around 4%, where it remained until spring 2012, when it suddenly doubled to around 7-8%, where it has remained since. Although the Eurozone was yet again in the news around this time with a second bailout for Greece, the likeliest explanation for this second surge was domestic politics: UKIP’s rise coincided with a sharp drop in Conservative support in the wake of the “omnishambles” budget and other political scandals and set backs. UKIP seem to have been the big beneficiary from this opinion shift, and have retained their added support as public opinion settled down over the summer, leaving them within striking distance of the Liberal Democrats.

While UKIP’s story is one of advance in two spurts, the Liberal Democrats’ story since joining the Coalition is one of decline followed by stagnation. Our estimates suggest the party’s decision to ally with the Conservatives, and then to support policies such as tuition fee increases which they had opposed prior to Coalition, has decimated their support. From a peak of close to 25% immediately after the election, the Lib Dems fell relentlessly to a level of around 8% at the end of 2010, losing two thirds of their former support and have been stuck at this level ever since. The good news for Clegg and his party is that what remains of their support seems to be pretty loyal – their support has not shifted at all in the last 18 months despite steadily declining rating for the government in general, and Nick Clegg in particular. The bad news is that support has stablised at a level which would bring annihilation in a general election, as it already has in local and Scottish elections. No wonder Nick Clegg feels the need to say “sorry”.

UKIP’s surge and the Lib Dems collapse has added an intriguing undercard fight to the tradition main event of Labour vs Conservative. Can Nigel Farage’s blazered and pinstriped Brussels bashers really overtake the dominant third force in British politics for a generation? Current polling suggests it is certainly possible, but there are also reasons for skepticism. Firstly, Liberal Democrat MPs may be able to fall back on their local popularity to offset the effects of their party’s national toxicity. MPs generally enjoy some incumbency bonus, reflecting their profile and popularity among local constituents, and Liberal Democrats may enjoy a larger than typical advantage here. Many represent seats in areas which on paper look like hostile territory – such as Simon Hughes in normally heavily Labour inner London or Chris Huhne in Eastleigh, a formerly deep blue Hampshire seat. Such seats were often won on a large anti-government swing at by-election and then held through assiduous local service by MPs unusually well aware that they need to win and hold local loyalties to survive. Incumbent who have cultivated strong local roots of this kind may perform better than the polls suggest.

The Liberal Democrats also understand better than UKIP the hard realities of electoral geography. It is no use in British politics getting 20% of the vote in every seat – you are left with a large crop of losing candidates, a grievance against the electoral system, and no political representation at all. Returning MPs to Westminster requires geographically concentrated support, which for an insurgent party normally means a long slog in local politics, building a profile and an activist base to enable a break through at Westminster. Many Lib Dem MPs owe their support either to intensive local work of this kind, or to the residual Liberal loyalties of areas like South West England and the Scottish Highlands, which have been returning Liberal MP’s since William Gladstone’s time.

Building such a local support base will also be vital for UKIP, as their support is unusually evenly spread. Although UKIP won close to a million votes in 2010, they did not get more than 10% in any seat contested by the main parties, and only managed three third place finishes. Those predicting a UKIP surge in Westminster should remember there are no seats at all in Britain where UKIP are the main challenger to the incumbent. It might be possible to overcome such a position with a determined, locally focussed activist push, perhaps beginning in the South Western districts where UKIP has performed strongest in the past. But, as yet, there is little evidence of a serious push by UKIP to build strong local profiles. Although the party won record levels of support in the 2011 and 2012 local elections, this was once again spread evenly over the country, and UKIP still has no representatives on any of Britain’s district or metropolitan councils, and only a smattering of representatives on smaller, lower profile town councils (often through defection rather than election).

Without concentrated local bases of support and activism it will be very hard for UKIP to break through nationally in the next general election. How many of UKIP’s new supporters will remain willing to support an unknown candidate wearing the rosette of a party which came fourth in the last election and has never managed to even elect a local councillor? UKIP’s poll ratings are impressive, and probably sufficient to deliver another strong showing in the 2014 European Parliament elections, but without local strongholds it remains likely that the purple tide will recede when voters come to elect their new MPs in 2015.